1. Field of the Invention
The present invention relates generally to the field of loudspeakers, and in particular, to a voice coil adaptor ring for mating the cone and spider for increased strength and efficiency.
2. Description of Related Art
Improved loudspeaker performance and more shallow speaker designs are constant goals in the car audio market. Simultaneously achieving these goals is difficult. To improve performance, higher excursions and more reliable suspension systems are desired, but require deeper speaker dimensions. Since mounting space in automobiles is limited, larger speaker dimensions are undesirable. In addition, physical clearance limitations for the speaker's moving assembly make it difficult to decrease the speaker's depth. Adequate clearance for the moving assembly is needed between the spider and top plate and the voice coil and bottom/back plate, as discussed more fully herein. Because of these and other limitations, achieving a more shallow speaker without compromising excursion and performance has been difficult. Accordingly, a loudspeaker with enhanced performance and a more shallow design would be well received. Thus, there exists a need for a speaker having these attributes. For a better understanding on how the instant invention addresses these needs, a discussion of general speaker construction follows.
With reference to FIG. 1, a conventional loudspeaker 20 generally comprises a support frame 22, a cone 24 with or without a dust cap 26 bridging across the cone 24, a suspension system, a voice coil 40, a voice coil bobbin/former 43, a top plate 37, a back/bottom plate 39, and a vented pole piece 41. Sometimes the cap comprises an integral part of the cone. The voice coil 40 is wound about the voice coil former 43 which resides in a defined annular magnetic gap. The magnetic circuit linearly cycles or displaces the voice coil former 43 in this gap. In the conventional speaker, the cone 24 is attached to the voice coil former above the coil 40 at its lower end and to the frame at its upper end. The back/bottom plate 39 is sometimes bumped or stepped, as opposed to flat, to increase excursion by allowing the voice coil 40 to travel below the magnet without making contact and causing damage. That is, additional clearance is obtained. However, a stepped/bumped back plate is more expensive to make. Also, bumped back plates have bump depth limits and can only be made so deep due to production methods. As a consequence, the designer may need to stack magnets for increased voice coil-to-back plate clearance. However, extra magnets are expensive, and may result in undesirable changes in motor system behavior, such as too much motor strength for the desired application.
Something inherent in every speaker is the magnetic gap center line. The magnetic gap is defined by the top plate and pole piece of the loudspeaker. The magnetic gap height is generally taken as the thickness of the top plate. Therefore, assuming uniform flux density across the air gap (an idealized, but practical premise), the magnetic gap center line bisects the top plate's thickness.
The suspension system of the loudspeaker controls linear motion of the cone and provides a major centering force for preventing the voice coil from rubbing and rocking against the pole piece. The suspension system normally comprises a surround 28 (upper or outer suspension) and a spider 38 (lower or inner suspension). The surround 28 is a mechanical device which holds the outer edge of the diaphragm/cone of the loudspeaker and is often referred to as a "roll." One purpose of the surround is to help keep the cone 24 centered and to provide an upper portion of the restoring force that keeps the voice coil in the magnetic gap. The surround also provides a damped termination for the edge of the cone. The spider 38 comprises a lower/inner suspension member that helps to keep the voice coil concentric to the pole piece. The spider also provides a portion of the restoring force that maintains the voice coil within the magnetic gap. Thus, the stiffness and structural integrity of the spider can greatly affect the loudspeaker's resonance. The spider also provides a barrier for keeping foreign particles away from the gap area. A spider 38 is commonly constructed from treated corrugated fabric.
In conventional loudspeakers, the cone and spider make a sheer attachment directly to the voice coil. That is, the cone and spider are adhered with glue to the vertical, cylindrical surface of the voice coil without any mechanical anchor or reinforcement. This results in a relatively weak adhesive joint. Therefore, the possibility of mechanical failures in the cone and spider is likely since the stress distribution around the glue joint is high.
In speakers having smaller voice coils, the inherent weakness of the glue joint is more critical. Spiders are typically made from resin treated cloth materials. When the inner diameter of the spider gets smaller, fewer strands of material intersect the cutout. Since the glue joint lies on this small circumference, very little spider material is captured. This places the spider material under greater stress than normal. This high-stress condition could cause the spider itself to fatigue prematurely. Since the spider is typically called on to center the moving assembly and limit cone motion at the extremes of excursion, a compromised spider could cause a catastrophic failure.
Another problem associated with conventional speakers is that they require pole vents for venting air pressure. Pole vents comprise holes bored directly through the pole piece 41. These vents are used to relieve air pressure that builds up beneath the cone volume. Without a pole vent, audible noise can be introduced as the trapped air under the dust cap tries to escape during large cone excursions. However, in speakers having a small diameter voice coil, the amount of metal in the pole piece can limit the magnetic flux in the speaker. Consequently, using a pole piece with large amounts of metal removed for pole vents can radically alter the performance of the magnetic circuit.
A vented pole piece further affects the thermal behavior of the speaker. The steel contained in the pole piece provides an effective thermal sink for the voice coil. Machining a pole vent in the pole piece increases thermal resistance of the sink, lowering the power handling capability of the loudspeaker.
In addition to the foregoing, the conventional speaker has inherent limitations which has made it difficult to achieve enhanced or sustained speaker performance in a shallow speaker design. Adequate clearance is needed between the voice coil and back plate and the spider and top plate for cycling the moving assembly. The positioning and shape of the top plate is also important as it affects clearance and the positioning of the magnetic center line. The spider suspension needs to be attached at points which facilitate decreased depth. Finally, decreasing the depth of a speaker can affect the positioning of the magnetic gap center line. In contrast with the present invention, the background art has failed to address or solve these issues.
A vented adaptor ring and modified top plate system, in accordance with the disclosure herein, is not contemplated by known speaker designs and would solve the above-noted problems. Several loudspeaker designs are contemplated in the background art; however, none of these references solve the above-noted needs. For example, Mitobe (U.S. Pat. No. 5,111,510) discloses a speaker and manufacturing method therefor including a diaphragm integrally combined with a first frame piece and a driver unit integrally combined with a second frame piece. Saiki et al. (U.S. Pat. No. 5,371,805) discloses a speaker and speaker system comprising a diaphragm secured to a first periphery of an edge member and a frame secured to a second periphery of the edge member. Scholz (U.S. Pat. No. 5,323,469) discloses a conical loudspeaker having a conical stabilizing element joined between an underside of a speaker membrane and an outside surface of a speaker moving coil carrier. Kreitmeier (U.S. Pat. No. 5,424,496) discloses an electromagnetic converter comprising an internal magnet system, a moving coil and tubular segment. Kreitmeier (U.S. Pat. No. 4,764,968) discloses a disk-like diaphragm made from a conical plastic film and provided with vacuum formed support members which extend up to the disk-like radiating layer. Kobayashi (U.S. Pat. No. 4,118,605) discloses a voice coil mount structure comprising a cylindrical member, which secures a diaphragm, a damper, and a coil winding. Bank et al. (U.S. Pat. No. 4,680,800) discloses a build ring that is mounted to the voice coil and secures the diaphragm and spider. Kobayashi and Bank, as well as the other noted references, do not provide any structure for ventilating air pressure from beneath the cone volume, or structure that facilitates the design of a shallow speaker without compromising performance.
The problems recited in the background art are addressed by the invention in the parent case, U.S. application Ser. No. 08/580,764. Although the parent invention solves many problems associated with high excursion loudspeakers and spider attachment, the inventor herein has discovered additional structure which improves loudspeaker performance and reliability in shallow speaker designs. The foregoing art fails to address the need for a high performance speaker in a shallow design. The depth of a loudspeaker, especially in the car audio market, is always in need of improvement. Decreasing the depth of a loudspeaker is limited by factors such as lack of clearance within the speaker, positioning and shape of the top plate, and location of the magnetic gap center line. The flat shape of typical top plates also limits the range of depth that can be sacrificed because of the location of the magnetic gap center line. The instant invention has adopted portions of the parent loudspeaker design and combined it with novel features to arrive at a unique, unobvious adaptor ring and speaker design that resolves the noted objectives.